Dr. Terry Gates, Ohio University – Geographic Isolation and North American Dinosaurs

In today’s Academic Minute, Dr. Terry Gates of Ohio University reveals how shifting geographic features contributed to the creation of two distinct groups of North American dinosaurs.

Terry Gates is Postdoctoral Fellow at the Ohio University Heritage College of Osteopathic Medicine and Research Scientist in the Department of Biology at North Carolina State University. He holds a Ph.D. from the University of Utah.

Seventy-five million years ago, North America was a very different place—warmer than today, split into three large islands by a flooding seaway, and inhabited by huge dinosaurs. The western island that is today the American and Canadian west preserves a huge array of dinosaur species, especially those of large-bodied plant eating horned dinosaurs and duck-billed dinosaurs, which are larger than elephants.

Interestingly, the time period just prior to the infamous K/T extinction, 65 million years ago, where all dinosaurs except birds went extinct, the number of these large plant-eating dinosaur species seems to have diminished. Paleontologists have questioned why for decades. Luckily, a revolution has started in dinosaur paleontology, where new species are being discovered faster than ever and are being placed within a time framework that allows direct comparison of dinosaur occurrences with geologic forces that may have affected their evolution.

My colleagues and I compared horned and duck-billed dinosaur species occurrences with geologic data on the rise of mountain chains in North America. We found that around 75 million years ago, the time when the flooding seaway and two mountain ranges coincided in the western continent, several closely related megaherbivorous dinosaur species lived simultaneously, but physically separated from each other. Also the rate at which new dinosaur species evolved skyrocketed during this same time. Later, when the seaway receded from the continent, evolutionary rates slowed dramatically. It seems the combination of physical barriers facilitated rapid evolution of dinosaurs for a short time in North America.

The amazing fossils found on this continent are quickly shedding new light on the dynamic evolution of dinosaurs in relation to changing climate and landscapes.